When an electromagnetic wave having a short wavelength of several tens of nanometers or less is dealt with, a difference in refractive index for any such electromagnetic wave between different materials is extremely small, specifically, 10−4 or less, and for example, a the critical angle for total reflection becomes extremely smaller. In view of the foregoing, a large-scale spatial optical system is usually used for controlling such electromagnetic wave including an X-ray. Among main parts of which the spatial optical system is formed is a multilayer mirror obtained by alternately laminating materials having different refractive indices, and this multilayer mirror is playing various roles such as beam shaping, spot size conversion, and wavelength selection.
A conventional X-ray waveguide such as a polycapillary propagates, in contrast to such spatial optical system, which has been in the mainstream, an X-ray by confining the X-ray in itself. Researches have been recently conducted on an X-ray waveguide, which propagates an X-ray by confining the X-ray in a thin film or a multilayer film with a view to reducing the size, and improving the performance, of an optical system.
Specifically, researches have been conducted on, for example, multiple X-ray waveguides each formed so that an X-ray is confined in a two-dimensional direction by total reflection, the X-ray waveguides being placed so as to be adjacent to each other (see NPL 1), and a thin-film waveguide of such a shape that a waveguide layer is interposed between two layers of one-dimensional periodic structures (see NPL 2).